Engines may use turbocharging to increase charge density and reduce engine displacement. Further, engines may use exhaust gas recirculation (EGR) to reduce NOx formation, increase fuel economy, and reduce knock. In one particular example, low pressure EGR systems may cooperate with a variable venturi to improve maximum EGR flow when desired based on operating conditions, where a low pressure EGR system is one that taps the exhaust at downstream of a turbocharger. The venturi creates vacuum to draw the exhaust into the engine air inlet stream.
The inventors herein have recognized that in addition to improving EGR operation, other vacuum-utilizing devices or systems may be coupled with the venturi in order to take advantage of its vacuum source; for example, the positive crankcase ventilation (PCV) system, the fuel vapor purge (FVP) system, or the vacuum amplifier for vacuum-powered actuators. For example, with regard to PCV systems coupled with the venturi it is possible to establish a single path PCV system (unidirectional) independent of fluctuations of the manifold pressure, even under boosted conditions. Likewise, when the fuel vapor purge system is coupled with the venturi, a single path (unidirectional) fuel vapor purge system may be established independent of fluctuations in manifold pressure, thereby avoiding reverse fuel canister purge flows.
However, the inventors herein have also recognized the interdependence in the configuration described above, where adjustment of one system can affect vacuum provided to, or flow of, another system. For example, changes in the EGR system and/or variable venturi can cause flow changes in the fuel vapor purging system.
Thus, in one approach, a method of controlling engine operation of an engine having an exhaust gas recirculation system and a fuel vapor purging system is provided. The method includes delivering exhaust gas recirculation flow from the exhaust gas recirculation system to a variable venturi coupled in an intake of the engine; delivering fuel vapor flow from the fuel vapor purging system to the variable venturi coupled in an intake of the engine; and coordinating adjustment of an exhaust gas recirculation valve coupled to the exhaust gas recirculation system, a fuel vapor purging valve coupled to the fuel vapor purging system, and the variable venturi in response to operating conditions.
In this way, it is possible to reduce inadvertent changes to fuel vapor purge flow (e.g., through adjustment of the fuel vapor purging valve) while maintaining desired EGR flow operation (e.g., through adjustment of the variable venturi and/or EGR valve).
While the above example relates to the particular situation of EGR and fuel vapor purging interacting with one another through the variable venturi, various other examples may be encountered as noted below herein. Further, the above examples may be applied to systems with two or more devices or systems coupled to the variable venturi.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.